Shotaro Shirai

All-microwave manipulation of superconducting qubits with a fixed-frequency transmon coupler

  1. Shotaro Shirai,
  2. Yuta Okubo,
  3. Kohei Matsuura,
  4. Alto Osada,
  5. Yasunobu Nakamura,
  6. and Atsushi Noguchi
All-microwave control of fixed-frequency superconducting quantum computing circuits is advantageous for minimizing the noise channels and wiring costs. Here we introduce a swap interaction
between two data transmons assisted by the third-order nonlinearity of a coupler transmon under a microwave drive. We model the interaction analytically and numerically and use it to implement an all-microwave controlled-Z gate. The gate based on the coupler-assisted swap transition maintains high drive efficiency and small residual interaction over a wide range of detuning between the data transmons.
arxiv pdf

Generating time-domain linear cluster state by recycling superconducting qubits

  1. Shotaro Shirai,
  2. Yu Zhou,
  3. Keiichi Sakata,
  4. Hiroto Mukai,
  5. and Jaw-Shen Tsai
Cluster states, a type of highly entangled state, are essential resources for quantum information processing. Here we demonstrated the generation of a time-domain linear cluster state
(t-LCS) using a superconducting quantum circuit consisting of only two transmon qubits. By recycling the physical qubits, the t-LCS equivalent up to four physical qubits was validated by quantum state tomography with fidelity of 59%. We further confirmed the true generation of t-LCS by examining the expectation value of an entanglement witness. Our demonstrated protocol of t-LCS generation allows efficient use of physical qubits which could lead to resource-efficient execution of quantum circuits on large scale.
arxiv pdf